REACTIONS TO ARGASID TICK BITES BY ISLAND RESIDENTS ON THE GREAT-BARRIER-REEF

Objective: To attribute a cause and quantify allergic-like symptoms observed among island residents. Design: Skin prick tests and intradermal injections with ultraviolet-irradiated, filtered (0.22-mu-m) whole-body homogenates of the soft tick, Ornithodoros capensis, were used to reproduce experimentally the symptoms observed. Setting: Heron Island, Great Barrier Reef, Australia. Participants: Island residents were designated as such after having spent more than 1 month on the island during the summer seabird breeding season. Interventions: Control measures were instigated using a residual insecticide, delta-methrin, sprayed inside sleeping quarters. Main outcome measures: Acaricide spraying reduced (X2 = 4.42; P < 0.05) the number of island residents complaining of having been bitten by ticks, yet was considered an inefficient control measure as 67% reported being attacked by ticks after spraying. Results: Among 97 island residents, elevated total IgE levels were associated with reaction to tick bite in 11 cases (X2 = 27.17; P < 0.001), but were not of reliable diagnostic value. Symptoms included intense pruritus, blistering (a major feature), erythema, weeping lesions, lymphangitis, dull ache, rheumatic pain and general lassitude, and intense discomfort. Sera from two of four volunteers with known reactions to O. capensis and one of four others with reactions to the Australian paralysis tick, Ixodes holocyclus, crossreacted with antigens from a total of four of six biting/stinging and non-biting arthropods (radioallergosorbent tests). Conclusions: Symptoms associated with reactions to tick bite peaked in severity at 35-40 hours and thus the response was most likely delayed type IV hypersensitivity.